linux-kernel - Re: [RFC 1/3] ARM: dts: imx28: Add description for L2 switch on XEA board

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Date:   Wed, 23 Jun 2021 17:26:31 +0200
From:   Lukasz Majewski <lukma@...x.de>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Madalin Bucur <madalin.bucur@....nxp.com>,
        Nicolas Ferre <nicolas.ferre@...rochip.com>,
        Joakim Zhang <qiangqing.zhang@....com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Vladimir Oltean <olteanv@...il.com>, netdev@...r.kernel.org,
        Arnd Bergmann <arnd@...db.de>,
        Mark Einon <mark.einon@...il.com>,
        NXP Linux Team <linux-imx@....com>,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC 1/3] ARM: dts: imx28: Add description for L2 switch on XEA
 board

Hi Andrew,

> On Tue, Jun 22, 2021 at 10:51:34PM +0200, Lukasz Majewski wrote:
> > Hi Andrew,
> > 
> > > On Tue, Jun 22, 2021 at 04:41:09PM +0200, Lukasz Majewski wrote:
> > > > The 'eth_switch' node is now extendfed to enable support for L2
> > > > switch.
> > > > 
> > > > Moreover, the mac[01] nodes are defined as well and linked to
> > > > the former with 'phy-handle' property.  
> > > 
> > > A phy-handle points to a phy, not a MAC! Don't abuse a well known
> > > DT property like this.
> > 
> > Ach.... You are right. I will change it.
> > 
> > Probably 'ethernet' property or 'link' will fit better?
> 
> You should first work on the overall architecture. I suspect you will
> end up with something more like the DSA binding, and not have the FEC
> nodes at all. Maybe the MDIO busses will appear under the switch?
> 
> Please don't put minimal changes to the FEC driver has your first
> goal. We want an architecture which is similar to other switchdev
> drivers. Maybe look at drivers/net/ethernet/ti/cpsw_new.c.

I'm a bit confused - as I thought that with switchdev API I could just
extend the current FEC driver to add bridge offload.
This patch series shows that it is doable with little changes
introduced.

However, now it looks like I would need to replace FEC driver and
rewrite it in a way similar to cpsw_new.c, so the switchdev could be
used for both cases - with and without L2 switch offload.

This would be probably conceptually correct, but i.MX FEC driver has
several issues to tackle:

- On some SoCs (vf610, imx287, etc.) the ENET-MAC ports don't have the
  same capabilities (eth1 is a bit special)

- Without switch we need to use DMA0 and DMA1 in the "bypass" switch
  mode (default). When switch is enabled we only use DMA0. The former
  case is best fitted with FEC driver instantiation. The latter with
  DSA or switchdev.

> The cpsw
> driver has an interesting past, it did things the wrong way for a long
> time, but the new switchdev driver has an architecture similar to what
> the FEC driver could be like.
> 
> 	Andrew

Maybe somebody from NXP can provide input to this discussion - for
example to sched some light on FEC driver (near) future.


Best regards,

Lukasz Majewski

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